The inventors of the present application have invented an optical-path-switching apparatus and a relevant method based on a new principle (see Patent Literature 1). The invented optical-path-switching apparatus is configured to irradiate a control-light-absorbing area of a thermal-lens-forming optical element with control light in a wavelength band that can be absorbed by the control-light-absorbing area and signal light in a wavelength band that cannot be absorbed by the control-light-absorbing area in such a manner that an optical axis of the control light coincides with an optical axis of the signal light when the control light and the signal light converge.
According to the above-described apparatus configuration, irradiation with the control light is selectively performed while the control-light-absorbing area of the thermal-lens-forming optical element is irradiated with the signal light. More specifically, in a case where irradiation with the control light and irradiation with the signal light are not performed simultaneously, the signal light passes through a hole of a mirror and travels straight.
On the other hand, if the irradiation with the control light and the irradiation with the signal light are performed simultaneously, the signal light is reflected by the hole-formed mirror that is inclined relative to the traveling direction of the signal light. In other words, the optical path of the signal light is changed by the mirror.
In this respect, Patent Literature 1 discloses an optically-controlled optical-path-switching apparatus that can switch the traveling direction of the signal light between two directions using the control light, which has only one type of wavelength. The optically-controlled optical-path-switching apparatus discussed in Patent Literature 1 is referred to as a “one-to-two type optically-controlled optical-path-switching apparatus” in the following description.
Further, the inventors of the present application have invented an optically-controlled optical-path-switching apparatus and a relevant light signal optical-path-switching method, in which a plurality of thermal-lens-forming optical elements are combined with hole-formed mirrors (see Patent Literature 2).
According to the invented optical-path-switching apparatus, a wavelength band that can be absorbed by a control-light-absorbing area and a wavelength of control light are in a one-to-one relationship. Further, the invented optical-path-switching apparatus uses a combination of a total of seven thermal-lens-forming optical elements, each having three types of control-light-absorbing areas; for example, there are used pigments that differ in absorption wavelength band.
In addition, the invented optical-path-switching apparatus realizes an optically-controlled switching system capable of distributing data of a server to eight destinations by ON-OFF controlling the control light having three types of wavelengths.
According to the above-described optical-path-switching apparatus discussed in Patent Literatures 1 and 2, a beam cross-sectional shape of the signal light is changed into a ring shape due to thermal lens effects obtained by the irradiation with the control light. Hence, the type of the above-described optical-path-switching is referred to as “ring beam type” in the following description.
Further, as disclosed in Patent Literatures 3 to 6, the inventors of the present application have further proposed other optical-path-changing methods and optical-path-switching apparatuses. According to the proposed optical-path-changing methods and the optical-path-switching apparatuses, emission of control light in a wavelength band that can be absorbed by the control-light-absorbing area and emission of signal light in a wavelength band that cannot be absorbed by the control-light-absorbing area are performed so as to let both the control light and the signal light enter the control-light-absorbing area of a thermal-lens-forming optical element and converge in the control-light-absorbing area. In this case, a light convergence point of the control light is differentiated from a light convergence point of the signal light.
Therefore, both the control light and the signal light converge on or near an incidence plane of the control-light-absorbing area in the light-traveling direction and then diffuse respectively. As a result, in the control-light-absorbing area, the temperature increases locally in the area where the control light is absorbed and its peripheral area. In response to the above-described increase in temperature, the structure of the thermal lens changes reversibly. The refractive index changes substantially, and the traveling direction of the signal light changes correspondingly.
According to the optical-path-changing mechanisms discussed in Patent Literatures 3 to 6, the signal light can retain a circular shape in beam cross section even in the case of irradiation with the control light. Hence, the above-described optical-path-changing mechanisms are referred to as “circular beam type.”
Each of Patent Literatures 4 and 5 discloses a one-to-two type optically-controlled optical-path-switching apparatus that can switch the traveling direction of light between two directions using the control light having a single wavelength. Further, each of Patent Literatures 5 and 6 discloses an optically-controlled optical-path-switching apparatus that can switch the optical path of signal light emitted, for example, from a central fiber of a seven-core optical fiber bundle between seven directions using the control light emitted from one of peripheral optical fibers provided around the central fiber. The optically-controlled optical-path-switching apparatus discussed in Patent Literatures 5 and 6 is referred to as “one-to-seven-type optically-controlled optical-path-switching apparatus” in the following description.
Further, in the conventional circular-beam-type optically-controlled optical-path-switching apparatus, especially in the one-to-seven-type optically-controlled optical-path-switching apparatus, the thermal-lens-forming optical element is irradiated with the control light and the signal light in such a manner that the control light and the signal light converge at different positions in the control-light-absorbing area. In this respect, employing an end face closely-arranged multi-core optical fiber bundle disclosed in Patent literature 7 is preferable because the positioning of the optical axis of a signal light beam as well as the optical axes of a plurality of control light beams can be simplified and it is feasible to avoid the usage of a dichromatic mirror that may adversely influence the polarization dependence.
Further, Patent Literature 8 discloses a thermal-lens-forming optical element that is capable of enhancing thermal lens effects, in addition to an explanation with respect to the viscosity of a solvent contained in a pigment solution to be used for the thermal-lens-forming optical element together with temperature characteristics thereof. Further, the optically-controlled optical-path-switching apparatus discussed in Patent Literature 6 uses the seven-core optical fiber bundle that can detect the signal light when the signal light is switched between, for example, seven directions.    Patent Literature 1: JP 3809908 B    Patent Literature 2: JP 3906926 B    Patent Literature 3: JP 2007-225825 A    Patent Literature 4: JP 2007-225826 A    Patent Literature 5: JP 2007-225827 A    Patent Literature 6: JP 2008-083095 A    Patent Literature 7: JP 2008-076685 A    Patent Literature 8: JP 2009-175164 A